The research proposed here continues our investigation of the role of affect in the development of preverbal communication and language. The central hypothesis that motivates and unifies the proposed research is that the infant's early affective responsiveness to the exaggerated intonation patterns characteristic of speech to infants gives the child initial access to meaning in adult speech and prepares the child for the later linguistic use of intonation to parse the speech stream and understand spoken language. To investigate this continuity between affective and linguistic communication, we need to address questions on several different levels: First, are the mapping relations between prosodic form and communicative function in adult speech to infants consistent and accessible to infants? Second, are preverbal infants selectively responsive to different prosodic patterns in adult speech? And finally, do the intonation contours of infant-directed speech actually facilitate language comprehension? The first objective of the proposed project is to conduct a series of 14 studies with infants to test the following hypotheses: a) In adult speech to preverbal infants, certain stereotypical prosodic forms are regularly associated with certain affective and communicative functions; b) In the preverbal period, infants show auditory preferences and selective cardiac orienting to characteristic pitch patterns in parental speech; c) The infant makes use of the exaggerated intonation contours in parental speech to facilitate language comprehension; d) When prosodic and semantic cues in form, while infants in the second year attend increasingly to semantic content. The second objective is to provide new evidence for a model of the development of communication which integrates perceptual, emotional, and linguistic processes. The third objective is to apply new experimental procedures to the study of language development, a research area that has relied traditionally on observational techniques. The studies proposed here are conceptually integrated yet methodologically diverse, combining the richness of naturalistic observations with the control of laboratory procedures, in order to yield convergent evidence on affective processes in the transition from preverbal to verbal communication.